Conventionally, an ophthalmic lens such as a contact lens or an intraocular lens is provided with an identifying mark in the form of characters, figures, symbols, etc., principally for easy distinction between the front and back surfaces of the lens or between lenses for the left and right eyes, and/or indicating the specifications of the lens, for instance. For marking the ophthalmic lens, there are known a printing method, a laser marking method, etc.
In the printing method, the ophthalmic lens is partially dyed or colored with a printing liquid containing a dye or a dyeing solution (ink). In general, the ophthalmic lens is dyed or colored by a screen printing method which uses a screen or stencil that is patterned so as to correspond to a desired identifying mark to be formed. The identifying mark formed by the printing method using the dye tends to gradually disappear or peel off due to various treatments repeatedly conducted on the lens such as cleaning of the lens by rubbing and boiling of the lens for disinfection. In view of this, various techniques have been proposed to improve the durability of the identifying mark of the lens under severe environments of use. For instance, the identifying mark is formed by coloring or dyeing the lens with the ink which permeates into the material of the lens, or the identifying mark is fixed to an inner portion of the lens with a chemical reaction of the lens material with the ink which has permeated into the lens material. In the above-described printing method employed for marking the ophthalmic lens, however, the dye may get in the polymer of the lens, and may be contained in the ophthalmic lens, causing a problem of insufficient safety.
The printing method by which the identifying mark is directly formed using the ink or dye as described above inevitably increases the number of process steps for marking the ophthalmic lens and requires additional steps and devices such as a drying step and a device for drying the ink or dye after the printing step. In addition, the ophthalmic lens needs to be handled frequently, undesirably resulting in a high defect or reject ratio of the ophthalmic lens. Accordingly, the cost of manufacture of the ophthalmic lens is undesirably increased, causing a problem of poor economy.
Examples of the laser marking method are disclosed in JP-B-62-37368 and JP-A-64-13520 wherein an ophthalmic lens is irradiated with a laser radiation, so that a mark is engraved in the lens surface. Another example of the laser marking method is disclosed in JP-B-5-67932 wherein a mark in the form of recesses and protrusions is formed, by a laser radiation, in a mold for molding a lens so that the lens formed in the mold has a mark on its surface, which mark corresponds to the recesses and protrusions of the mold. In the former method wherein the mark is engraved by the laser radiation, the thickness of the engraved or marked portions of the lens is inevitably reduced if the depth of engraving by the laser radiation is made relatively large in an attempt to attain a high degree of clarity or visibility of the mark. In this case, the strength of the ophthalmic lens is reduced, and the ophthalmic lens tends to be easily broken. Further, deposits (contaminants, stains) are likely to accumulate in the engraved or marked portions in the form of grooves or recesses, causing undesirable troubles such as irritation of the eye of the lens user. In the latter method wherein the mark is formed on the lens surface corresponding to the recesses and protrusions of the mold, the mark in the form of protrusions formed on the front surface of the ophthalmic lens is in contact with the inner surface of the eyelid during wearing of the lens, so that the lens user may feel uncomfortable. Even if the size of the mark and the amount of protrusion of the mark are made relatively small, it is impossible to completely get rid of the feeling of discomfort.